The Soviet team is trying to excavate the ruins of Babylon to find a weapon more powerful than the nuclear bomb, by going to a parallel dimension and visiting the Babylonian god Marduk, naturally. Turns out the tower of Babel was originally where some kind of powerful machine was housed, but people were too scared of it so they broke it apart, along with the tower.

Indy tries to gather the pieces of the machine before the Soviets do, and eventually manages to collect them, but then both the leader of the Soviet operation and the CIA representative try to convince him to give the machine to their respective side. He doesn’t trust either, but literally decides the US is the lesser evil and hands it to the CIA lol

The CIA guys promptly open a gate to Marduk’s dimension with the engine and… OH NO! The head CIA guy is actually evil and wants to send the supposedly not evil CIA lady in to go and get Marduk on the side of the US. Indiana Jones kills the CIA guy but they end up accidentally going to the other dimension anyway. Indiana Jones beats up Marduk and manages to escape with CIA lady. Then they meet up with the leader of the Soviet expedition who they then get along with and the three of them go off to get drunk together.